Traditionally, inorganic materials have dominated the semiconductor industry. For example, silicon arsenide and gallium arsenide have been used as semiconductor materials, silicon dioxide has been used as an insulator material, and metals such as aluminum and copper have been used as electrode materials. In recent years, however, there has been an increasing research effort aimed at using organic materials rather than the traditional inorganic materials in semiconductor devices. Among other benefits, the use of organic materials may enable lower cost manufacturing of electronic devices, may enable large area applications, and may enable the use of flexible circuit supports for display backplanes or integrated circuits.
A variety of organic semiconductor materials have been considered, the most common being fused aromatic ring compounds as exemplified by tetracene, pentacene, bis(acenyl)acetylene, and acene-thiophenes; oligomeric materials containing thiophene or fluorene units; and polymeric materials such as regioregular poly(3-alkylthiophene). At least some of these organic semiconductor materials have performance characteristics such as charge-carrier mobility, on/off current ratios, and sub-threshold voltages that are comparable or superior to those of amorphous silicon-based devices. These materials usually need to be vapor deposited since they are not very soluble in most solvents.
Because of its good electronic performance characteristics, pentacene is often the organic semiconductor of choice. However, pentacene can be difficult to synthesize and purify. Because of the limited solubility of pentacene in many common solvents, semiconductor layers containing pentacene typically cannot be formed using solvent-based deposition techniques. As an additional complication for solvent-based deposition techniques, pentacene tends to oxidize or undergo dimerization reactions in many solutions. Once deposited in a semiconductor layer, pentacene can oxidize over time. This can lead to reduced performance or complete failure of the semiconductor device that contains the oxidized pentacene.